MIME::Parser versions before 5.521 for Perl set no limit on the number of message parts by default, allowing memory exhaustion. The max_parts option defaulted to -1, which disables the limit, so a parser created with default settings builds an entity for every part however many a message has. Version 5.521 sets max_parts to 1000 and max_depth to 64 by default. Setting either to -1 still removes the limit.